An example of a primary suspension system somewhat similar to the one involved in this application may be found in copending patent application entitled "Primary Suspension System for a Railway Car", Ser. No. 296,796, filed Aug. 27, 1981, assigned to the same assignee as the present invention.
There are presently in use railway cars in which the primary suspension system includes rubber so called shock rings fitted around the journal bearing assemblies between the bearing assemblies and the side frames of the truck. The rubber rings are compressed and clamped between the journals and side frames. Because of the arrangement used, very high vertical and longitudinal stiffnesses result, in the order of about 100,000 pounds per inch.
Relatively high vertical stiffness in the primary suspension systems results in very little attenuation of the wheel accelerations to the truck frame. The relatively high longitudinal stiffness tends to maintain the axle positions or wheel bases within the truck frame.
Tests have indicated that reducing the vertical stiffness in the primary suspension systems reduces the accelerations transmitted from the wheels to the truck frame. This tends to increase the useful life of the truck mounted equipment.
Tests have also indicated that reducing the longitudinal stiffness in the primary suspension system permits the axles on the truck to assume a more radial position with respect to the tracks when making turns. This reduces the angle of attack of the wheel flanges with respect to the tracks thereby reducing lateral wheel forces. The result is reduction of wheel and flange wear and longer life.
The aforementioned application discloses a primary suspension system including rubber rings disposed between wheel journal bearing assemblies and the side frame of a railway truck. The rubber rings have cut-away portions or openings therein bonded to inner and outer split metal rings. The openings in the rings provide relatively low spring rates for the suspension system.
While the suspension system of the aforementioned application is satisfactory, it is sometimes desirable to provide a soft spring rate up to a certain level and a somewhat harder spring rate beyond a certain level to accommodate very high loads and to minimize gross deflections during operation. This is because the rubber or elastomeric material with openings therein may not be able to carry the loads involved. At the same time, it is desirable that the changes in spring rate changes from a low spring rate to a high spring rate be accomplished smoothly without abrupt changes.